Beat egg yolks until thick and lemon colored.
Stir soda into buttermilk.
Mix buttermilk into egg yolks.
Stir together flour and sugar.
Mix sugar into egg mixture.
Stir in lemon extract.
Pour mixture into top of a double boiler.
Cook over hot water stirring constantly until mixture thickens.
Pour into pie shell.
Bake 25-30 minutes at 350°F. until custard is set.
Top with meringue and bake 8-10 minutes t 400°F until meringue is golden brown.